Current radio communication systems are developed such that they provide services requiring a high transfer rate, such as broadcast, multimedia images, multimedia messages, etc. Particularly, a new radio communication system capable of using a wider bandwidth and supporting a downlink maximum data rate of 1 Gbps and an uplink maximum data rate of 500 Mbps is being developed. With this development trend, newly developed radio communication systems introduce previously unused technologies. For example, introduction of an 8Tx downlink antenna construction technique, a 4Tx uplink antenna construction technique, a relay technique for improving the performance of a radio network, a carrier aggregation technique, an OFDMA transmission technique on an uplink, etc. is discussed to construct a new radio communication system.
With the improvement of system performance and introduction of new technology, structures such as a frame form and a physical signal system used on a radio channel may be changed. Accordingly, system equipment such as a base station performs communication with user equipment according to a new structure, and the user equipment need to perform communication in response to the new structure. However, it is difficult for all user equipment to operate according to the new structure in a moment, and thus a legacy system and a new system coexist. Accordingly, the new system needs to support both user equipment operating based on a legacy structure and user equipment operating based on the new structure. Therefore, an alternative for performing communication supporting the new structure while having backward compatibility with the legacy structure is required.